The present invention relates generally to improving performance of a pump-turbine unit. In particular, the invention relates to a technique for optimizing performance of pump-turbines by identifying wicket gate settings optimizing one or more operating parameters such as efficiency during a pumping mode of operation, cavitation, vibration and the like, capable of adversely affecting profitability or long term operation of the unit. The invention also permits optimal gate settings or data from which such settings may be determined to be associated with operating parameters defining the operating condition of the unit in a multi-dimensional virtual cam matrix for subsequent use when similar conditions are encountered.
Pump-turbine power generation techniques have become well established over recent decades as an alternative or complement to conventional turbine power production arrangements. Generally, pump-turbine machines include a set of wicket gates and a runner/impeller which can operate as a Francis-style turbine in one direction of rotation and as a centrifugal pump in an opposite direction. A motor-generator coupled to the pump turbine functions both as a power generator during a turbining mode of operation and as a motor or prime mover for the pump during a pumping mode.
Pump-turbine installations provide energy storage systems by utilizing excess electric capacity on power distribution grids in times of reduced energy demand to pump water, previously used to generate power, back into an upper reservoir. The water is then again used to generate electricity when needed, such as during peak demand periods. Pump-turbine units are presently in use over a wide range of heads and power output levels. The overall efficiency of pump-turbine units depends not only on the ability of the equipment to effectively produce power from water flow from the upper reservoir during the turbining mode of operation, but equally on its ability to efficiently move water back to the upper reservoir during the pumping mode. To maximize the cost effectiveness of the pump-turbine installation, it is therefore necessary to generate power as efficiently as possible during turbining, while utilizing as little power as possible for the needed water displacement during pumping.
Various techniques have been proposed and are currently in use for regulating operation of pump-turbine units during turbining and pumping modes of operation. In the pumping mode of operation, older governors position the wicket gates in a fixed, predetermined position to let water through the pump to the upper reservoir. However, because the pumping efficiency of the unit is influenced by the wicket gate position, the flow rate and the head across the unit, a single wicket gate position will generally not provide optimal efficiency for different flow rate and head conditions.
Other techniques are known that attempt to improve operation of the pump-turbine in similar manners for both phases of operation. For example, it is known to estimate desired wicket gate positional settings from test data generated on a small scale model for the installation. Such model test data may be used to establish a mechanical or computerized ("virtual") cam surface relating head, flow and power in such a way as to identify desired wicket gate settings. Surfaces, real or virtual, of this type are typically referred to as "3D CAMs." In the pumping mode of operation the power parameter represents the power input needed to drive the pump and thereby displace water at particular head and flow rates to the upper reservoir. It is also known to identify certain preferred wicket gate positions for the pumping mode of operation through special test sequences, such as index tests.
While model-based 3D CAM techniques are generally preferable to the fixed wicket gate approach, they fail to account for differences between model test performance and that of actual equipment. Where index testing is used to identify preferred wicket gate positions, such testing typically requires at least temporary interruption of normal service of the facility, and generally does not identify desired settings over a broad range of operating conditions. Moreover, model testing and index testing do not typically account for the impact of other parameters such as cavitation or vibration during pumping. Because modest improvements in performance can result in considerable gains in revenue for the installation, such drawbacks may amount to large real or opportunity costs for the plant.
There is a need, therefore, for an improved method of controlling pump-turbine installations that allows optimal wicket gate positions for pumping mode operation to be determined for actual operating equipment and during normal operation of the facility. In addition, there is a need for techniques of this type that can account for factors other than head, flow and power input in evaluating the desired gate positions.